Mixing enhancement via nozzle trailing edge modifications in a high speed rectangular jet

Abstract

An aspect ratio 3 rectangular nozzle with design Mach number 2 was used to investigate the effects of trailing edge modifications on mixing enhancement and to explore the sources of streamwise vorticity at the fully expanded jet Mach numbers 1.75, 2.0, and 2.5. The trailing edge modifications are simple cut-outs in the plane of the nozzle at the nozzle exit. The investigation of mixing and interaction between mixing layers and vortices was performed by the laser sheet illumination technique. Through surface flow visualizations and wall pressure measurements, the investigation of the major source of streamwise vorticity was carried out. In addition, the variation of thrust generated by the nozzle with modified trailing edges was investigated. In the underexpanded flow condition, the major source of streamwise vorticity was determined to be the spanwise surface pressure gradient on the modification. Substantial mixing enhancement was achieved in this flow regime. On the other hand, in the overexpanded flow regime, the role of streamwise vortices in mixing and the source of streamwise vorticity were unclear, and mixing enhancement was not substantial. No measurable thrust loss or gain was obtained for nozzles with trailing edge modifications, regardless of the type of modification.